1. Field
Embodiments of the present invention relate generally to gas turbine engines, and in particular, to a method and apparatus for supporting an aft portion of a transition duct in a gas turbine engine.
2. Description of the Related Art
A conventional gas turbine engine includes a compressor section, a combustion section including a plurality of combustors, and a turbine section. Ambient air is compressed in the compressor section and conveyed to the combustors in the combustion section. The combustors combine the compressed air with a fuel and ignite the mixture creating combustion products defining hot working gases that flow in a turbulent manner and at a high velocity. The working gases are routed to the turbine section via a plurality of transition ducts. Within the turbine section are rows of stationary vane assemblies and rotating blade assemblies. The rotating blade assemblies are coupled to a turbine rotor. As the working gases expand through the turbine section, the working gases cause the blades assemblies, and therefore the turbine rotor, to rotate. The turbine rotor may be linked to an electric generator, wherein the rotation of the turbine rotor can be used to produce electricity in the generator.
The transition ducts are positioned adjacent to the combustors and route the working gases from the combustors into the turbine section through turbine inlet structure associated with a first row vane assembly. The vane assembly is mounted on an annular vane carrier. The transition duct comprises an aft frame defining a transition exit that opens into the gas turbine section.
A transition duct may be assembled on the aft side by fastening the transition aft frame to a stator component of the turbine section, such as the vane carrier. For this purpose, the forward face of the vane carrier contains axially extending threaded holes or holes comprising threaded inserts that align with a central radially outwardly extending bracket of the transition aft frame. The transition aft frame is then bolted to the vane carrier.
At the forward end, the transition duct is attached to one of the combustors by a forward mount. To accommodate differential thermal growth between the combustor and the transition duct, the forward mount is generally compliant to a translation motion along the axis of the transition duct. At the aft end, the transition aft frame is vertically constrained by the bolts. However, bending of the central bracket of the transition aft frame allows horizontal or axial (with respect to the vane carrier) motion of the transition duct at the aft end.
The relatively unconstrained horizontal motion of the large mass transition duct, coupled with a vertical constraint from the transition aft frame imposes bending on the outer diameter surface of the transition duct. This causes cracking of the transition duct at the midspan of the outer diameter surface of the aft end of the transition duct.